It is generally thought that the fibrogenic effect of asbestos is dependent on its size, particularly its length. However, definitive studies have not been performed because of the lack of suitable techniques for size-classifying asbestos samples. Under the present grant, techniques are being developed to achieve length and/or diameter classifications of fibers. Based on the opposing-jet classification scheme developed by the principal investigator fibers are classified through parallel or perpendicular alignment to the orginal flow stream. Additional size classification characteristics through mechanical and fluid-dynamic excitation.